A New Laboratory Machine for Evaluating Breakdown Characteristics of Rubber Compounds R. S. HAVENHILL AND W. B. MACBRIDE, St. Joseph Lead Company Laboratories, Josephtown, Pa. must simulate service conditions, ITH t h e a d v e n t of A new laboratory flexometer for evaluating permit the evaluation of all the modern high-speed breakdown and blowout characteristics of rubber forces producing flexure, and acmechanical equipment compounds is described. This machine differs curately indicate the end point, manufactured by the automofrom previous machines in that the jlexing forces or initial f a i l u r e , of t h e test t i v e , r a i l w a y , electrical, and specimen. are measured at all times, and initial failure of other industries, there has reA study of several e x i s t i n g sulted an increase in the use of the sample is accurately indicated before comflexing machines (1, 2, 4) disrubber compounds for absorbplete blowout occurs. The test specimen w e d , closed that they do not coming vibration and eliminating 3.81 cm. in diameter and 3.81 cm. in length, is pletely fulfill the above condishock and noise. Quick acrotated between two parallel plates, the buse betions. On none of these machines celeration, high speeds, rapid apis it possible to measure all the ing off-center referred to the top. Stocks m a y be plication of brakes, and h e a v y flexing forces, and the end point live loads, in both mobile and compared under condilions of “constant load” or or initial failure of the test specistationary equipment, have im“constant deflection.” menis not indicated. Attempts posed severe distortional and deBy means of this machine it has been found to measure the power required to structive stresses on rubber parts. that the jlexing force does not decrease as the break down the s p e c i m e n by The heat generated in many of means of wattmeters or other sample is flexed, but actually increases, indicating these parts, such as solid tires, power-measuring devices have carcass stocks, and various methat a marked structural change has taken place been defeated because of the low chanical goods, is sufficient to in the rubber. The effects o n breakdown charmechanical efficiency of the app r o d u c e decomposition of the acteristics due to changes in volume loading, type paratus. rubber compound, resulting in of pigment, and other compounding variations are Since none of the above maactual blowout. In other inchines fulfilled all the requireshown. Tests o n commercial stocks show good stances the stocks take on an exments, the authors’ technical cessive p e r m a n e n t set which correlation with road tests on tire and carcass organization undertook the decauses severe misalignment of compounds. sign and construction of a maparts, The c o m p o u n d e r has ”-chine incorDoratina the desirable found it necessary to use all the skill and ingenuity a t his command to cope with these features. It was believed that the flexing forcescould be more conditions. Zinc oxides are used in large percentages in many conveniently measured if the test specimen were rotated. A of these compounds and it has been found that various zinc cylindrical test specimen rotating a t 875 r. p. m. is used. oxides give different performance results. DESCRIPTION OF MACHINE To develop zinc oxides and rubber compounds which will better withstand the more severe conditions, a flexing machine Figure 1, a drawing of the complete machine, shows the is of considerable value. To be of utmost value this machine mechanism for loading and flexing the test specimen, as well as the means by which the flexure and flexing forces are measured.
W
Test specimen 1 is accurately positioned between face plates 2 and 3 through use of centering jig 4. By release of jack 5, the load is applied vertically to the test specimen from weights 6, acting through lever arm 7, which rests on top of vertical shaft 8, producing compression in the test specimen. This shaft is driven by pulley 9 which is belted t o a vertical shaft motor. The lowrr face late, 3, rests on vertical shaft 10 and is driven by the upper staft and face through the test specimen which acts as a coupling. Vertical shaft 10 and carriage 11are mounted on rollers 12 that ride on track 13. FIGURE 1. DIAGRAM OF MACHINE 1. Rubber test specimen 2. Upper face plate 3. Lower face plate 4. Centering jig 5 . Hydraulic jack 6. Vertical load weights 7. Lever 8. Upper vertical shaft 9 V-belt pulley 10: Lower vertical shaft 11. Carriage 12. Carriage rollers 13. Track 14. Hydraulic jack
J 60
15.
16. 17. 18. 19. 20. 21. 22.
23. 24. 26. 26.
27.
Horizontal load weights Hanger for weights Bell crank Link for deflection adjuatm Handwheel Platform scale lent Parallel linkage Double divided s c a l ~ Straight edge for micrometer Pointer for vertical compre8sjon Pointer for horizontal deflection Dial-type micrometer gage Carriage atop
January 15, 1935
61
ANALYTICAL EDITION
In addition to the vertical compression,' horizontal deflection is produced in the test specimen by release of jack 14 which allows weights 15, acting through hanger 16, bell crank 17, and link 18, to move carriage with face plate 3 horizontally to the right along track 13. Weights 15 rest on platform of scale 19 during the progress of the test. Changes in the horizontal deflecting force and the initial failure are indicated by this scale. This
FIGURE 2. COMPLETE MACHINE Drive and all mechanism for loading and flexing the specimen, also devices for measuring the flexure and flexing forces.
platform scale is used in all tests except the stepped-increase horizontal load test, when it is removed and suitable dead weights are added to hanger 16 at chosen intervals. Changes in horizontal deflection are made by adjusting handwheel 20 which changes the length of hanger 16. Up er shaft 8 is maintained vertically by parallel linkages 21 a n 1 the axes of upper and lower shaft are parallel throughout the test. From a study of Figure 1 it is evident that the vertical load may be varied to suit different conditions of testing by changing weight 6, and that changes in horizontal deflection and horizontal load may be made by suitable adjustment of handwheel 20. The design permits modifications whereby the vertical or horizontal load, or both, may be held constant, resulting in variable deflections, or the deflections may be held constant, resulting in variable loads. Changes in vertical compression and horizontal deflection of the test specimen may be observed throughout the test by means of double divided scale 22, straight edge 23, pointers 24 and 25, and dial-type micrometer gage 26. Scale 22 and straight edge 23 are attached to the upper assembly, while pointers 24 and 25 and micrometer gage 26 are attached to the lower assembly. Pointer 24 indicates the vertical compression of the specimen on horizontal graduations of scale 22, while pointer 25 indicates the horizontal deflections on vertical graduations of scale 22. The horizontal deflection may be more accurately measured by using straight edge 23 and dial-type micrometer gage 26 which is readable t o 0.00127 cm. (0.0005 inch). Jack 14 is used to return the lower face plate 3 with carriage 11 to concentric alignment with upper face plate 2. Stop 27 prevents over-travel of the carriage. Jack 5 raises the upper assembly for the removal or insertion of test specimens. Figure 2 is a photograph of the complete machine. Figure 3 is a close-up of the machine, showing the test specimen running under vertical compression and horizontal deflection. Plates 2 and 3 are faced with a Bakelite Micarta compound, chosen to obtain a balance between the applied mechanical loads and the thermal retention which would most nearly simulate the usual service conditions. An asbestos fabric compound was chosen for its ability to stand up under high temperature without deterioration. Figure 4 gives the effects of two different Micarta compounds when identical specimens were used. Compound 256 deteriorated rapidly and was discarded in favor of No. 200.
TESTSPECIMENS The specimens (Figure 5, A ) used in all the tests recorded in this paper were 3.81 cm. (1.5 inch) in diameter and 3.81 em. (1.5 inch) high and cured in the laboratory in an eightcavity mold, Specimens of other sizes and shapes may be cut from cured articles. For comparison, the size and shape of the specimens in any series of tests must be identical and circular symmetrical specimens are preferable. The uncured stock is sheeted out on a 15.2 X 30.5 cm. (6 X 12 inch) laboratory mill to about 0.381 cm. (0.15 inch) in thickness. Strips 5.72 em. (2.25 inch) wide, with a length equal to the width of the sheeted stock, are cut off and rolled up with the grain of the rubber parallel to the axis of the cylinder. As in tensile testing, grain direction markedly affects the results, in some instances causing variations of 50 to 100 per cent, making it necessary t o have the grain always in the same direction.
TESTING PROCEDURE Testing under high vertical loads and high horizontal deflections sets up disruptive forces in the specimens which result in early breakdown and unsatisfactory data. Some specimens failed in 2 minutes when excessive vertical loads and horizontal deflections were applied. Tests conducted for a duration of 30 to 60 minutes are desirable. The type of test determines the procedure, which generally consists in adjusting the machine for proper loads and deflections, and taking and recording readings of vertical compression ( V C ) , horizontal deflection ( H D ) , and horizontal load ( H L ) a t appropriate intervals, usually 2 to 5 minutes until failure occurs.
FIGURE3. CLOSE-UPOF MACHINEWITH THE SPECIMEN RUNNING UNDER LOAD AND DEFLECTION Gages and scales for determining vertical compression and horizontal deflection are clearly shown.
The temperature of the face plates (2 and 3, Figure 1) at start of the test has a marked effect on the results. Before any tests are conducted, a dummy specimen is run in the usual way to bring the plates to operating temperature. Tests are started with a face plate temperature of 57.2" to 62.8"C. (135" to 145"F.). The temperature is measured by a copper-constantan thermocouple a t the start of each test. During the test the temperature of the specimen may be taken at failure, or any intermediate point, by stopping the machine and inserting a modified hypodermic thermocouple into the center of the specimen. The machine is readily adapted to a wide variety of testing conditions :
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
62
CONSTANT HORIZONTAL DEFLECTION.Constant vertical load resulting in variable compression. constant vertical compression resulting in variable load; variabie horizontal load; and measurement of flexure set. CONSTANT HORIZONTAL LOAD. Constant vertical load resulting in variable com ression; constant vertical compression resulting in variable loaf; variable horizontal deflection-stepped increase horizontal load and matched horizontal load-and measurement of flexure set. For flexure set test, specimens are removed from the machine..before initial failure and the percentage decrease in thickness is determined.
Cotton abric 200 A
v
/I
Y
I
I
I
I
I
aMc
I I
0
Vol. 7 , No. 1
5, E ) , which is indicated by a sudden decrease in the load (Figure 7) or, in exceptional cases, by a failure of the load to increase. If a test is continued beyond this point the load further decreases until blowout of the specimen, which may occur within a few seconds or many minutes. Experience has indicated that tests carried to complete destruction are not indicative of the service life of a rubber compound. Since the point of initial faiIure can be accurately determined, the authors’ tests are not run to complete destruction or blowout. Figure 7 shows constant horizontal deflection test data on two identical specimens run to complete blowout. Correlation is good as regards initial failure and poor as regards blowout. The increase in horizontal load occurs with an increase in vertical compression, or flattening, of the specimen which was a t first thought to cause the increase in load. Tests (Figure 16) conducted with a constant vertical compression and constant horizontal deflection show that the horizontal load increased as before and was not due to the change in shape of the test specimen, The increase in horizontal load is probably due to a continuous change in permanent set as well as to an increasing stiffness and change in the properties of the rubber compound as the temperature of the specimen increases. A study of the rotating specimen with the stroboscope reveals very little torsion. It was thought that this might affect the horizontal load, but even excessive torsion produced by braking the lonTer face plate until slippage occurred had little or no effect.
CONSTANTHORIZONTAL DEFLECTIONTESTS. In this method of testing, the desired horizontal deflection is set by means of handwheel 20 (Figure l),and no further adjustments in this deflection are made in any series of comparable tests. The test specimen is centered in the machine by means of jig 4. Vertical load weights 6, acting on upper plate 2, are allowed to compress the specimen by release of jack 5 . After the machine is started, rotating face 3 is pulled off-center (horizontally deflected) from rotating face 2 by release of jack 14. Readings of vertical compression, horizontal deflection, and horizontal load are taken at regular intervals and properly recorded. As upper face plate 2 and assembly drop down during the progress of the test they also move t o the right, as parallel linkages 21 describe an arc in the downward travel. Also with an increase in horizontal load, weights 15 resting on platform of scale 19 rise, because of a lessening of the load on the scale which causes lower face plate 3 and carriage to move t o the left. The effect of these movements is to decrease slightly the horizontal deflection applied t o the test specimen. This condition might be interpreted as creating a considerable source of error, but when similar stocks are compared the net differences in horizontal deflections at comparable periods are extremely small. If it is desirable to maintain this deflection constant throughout the test, this is accomplished by frequent adjustment of handwheel 20 and reference to the dial-type micrometer gage. Table I and Figure 6 show these differences.
TYPESOF BREAKFIGURE 5. REPRESENTATIVE DOWN PRODUCED BY NEWMACHINE A . Original rubber test specimen B. First degree of permanent set; specimen removed from machine a t about one-third breakdown time C. Second degree of permanent set; specimen removed from machine a t about one-half breakdown time D. Third degree of permanent set on undercured stock E. Initial failure, showing the porous center which is the first indication of breakdown, as,shown by a decrease in horizontal load. Typical of high-zinc stocks F. Breakdown, split type; generally follows type E. Typical of high-zinc stocks G. Sticky decomposed center type, characteristic of gas-black stocks, such as pneumatic tire treads H . Mechanical breakdown or blowout due t o excessive vertical lnad and horizontal deflection
HORIZONTAL DEFLECTION TESTS TABLEI. CONSTANT Breakdown data on zinc oxides A, B, and C VL,261 kg. H D , 0.714 om. VERTICAL HORIZONTAL DEOXIDE
Start of test
A B
C Half breakdown Breakdown
TIME Min. 0
COMRRBSSION
FLECTION
CnZ.
Cm ,
0
0
A B
8;::
0.940
C
28.5
1.316
57.0
1.930
6C
2;:
i:;:
: :E
LOAD Kg.
:!:; 16.2 ~:~~~ i::; 0.691
0.660
26.5
0.620
34.0
::ti!
During these tests the horizontal load necessary to deflect the specimen increases in value until initial failure (Figure
An autographic attachment is being designed which will automatically record the vertical compression and horizontal load and stop the machine when initial failure occurs. Other changes are also contemplated which will practically eliminate the variation in horizontal deflection. CONSTANTHORIZONTAL LOADTESTS. If the platform scale be removed and a dead weight sufficient to produce failure be used for horizontal loading, the specimen is pulled out of the machine because of excessive horizontal deflection. If, then, a dead weight be used which can be sustained by the specimen a t the start of the test, a progressive stiffening of the stock takes place during test which actually lifts the dead weights and results in decrease of the horizontal de-
.
ANALYTICAL EDITION
January 15, 1935
63
Chanqa t i Horkantal Deflect on During Test
=
:=so0
start of Test
Halfay
Finish of Test
FIGURE6. CONSTANT HORIZONTAL DEFLECTION TEST Zinc oxides A, B, and C Tire in Minutes
flection to a point where no failure is possible even under proFIGURE7. CONSTANT HORIZONTAL DEFLECTION TEST longed testing. Zinc oxide A Since Failure is not possible under the conditions outlined above, tests are conducted with a stepped increase in the BREAKDOWN TESTDATA horizontal load. Platform scale 19 is removed from the machine and weights 15 are allowed to hang free during the CONSTANT HORIZONTAL DEFLECTION TEST. Figures 13, test. These weights are adjusted to the maximum that the 14, and 15 and Table I show breakdown test data on stocks specimen will sustain a t the start of the test. At regular time containing the various oxides. A 261-kg. (575-lb.) constant intervals the weight is increased by certain increments until vertical load and a 0.714-cm. (0.281-inch) horizontal deflecfailure occurs. In this test the stocks are compared under tion were applied to the specimen during these tests. identical loading conditions and the horizontal deflection is dependent on the modulus, stiffness, etc., of the rubber comTABLE111. STEPPED INCREASE HORIZONTAL LOADTESTS pound. (For stepped increase horizontal load test data see Breakdown data on zinc oxides A, B, and C Vertical load = 261 kg. Figures 17 and 29 and Table 111.) VERTICALHORIZONTAL An alternate method of comparing two or more stocks under COMDE- HORIZONTAL OXIDE TIME PRESSION FLECTION LOAD^ the same loading conditions is to run them under the constant M i n . Cm. Cm. KP. horizontal deflection test conditions as outlined above and Start of teat A 0 0.930 0.676 17.0 B 0 1.113 1.461 17.0 then retest, matching the horizontal load-time curves one to C 0 1.016 1.067 17.0 the other by continuous adjustment of handwheel 20, Figure Half breakdown A 11.8 1.034 0.663 23.1 1. This is known as the matched horizontal load test. B 12.0 1.481 0.605 23.1 C 9.6 1.113 0.630 17.0 RESULTSOF TESTS. The value and scope of the machine Breakdown A 23.5 1.387 0.737 35.4 B 24.0 1.626 0.663 35.4 are demonstrated by tests conducted on stocks containing C 19.2 1.288 0.813 29.3 various zinc oxides, and on commercial stocks furnished by Min. Kg. several rubber companies. The effect of cure and variations a Horizontal load 0-10.0 17.0 10.5-15.0 23.1 in compounding, such as particle size of zinc oxide and volume 15.6-20.0 29.3 loading, is shown. The effect of changes in vertical load, 20.5-26.0 35.4 vertical compression, horizontal load, and horizontal deflection is also shown. Fine, medium, or coarse zinc oxides were used in all t h e s p e c i m e n s tested and were compounded with the r u b b e r a c c o r d i n g to the formula given in Table 11, the only exceptions being the commercial stocks furnished by the manufacturers. A B C Photomicrographs of these zinc oxides are shown in FigFIGURE8. PHOTONICROGRAPHS ( X 1500) OF ZINC OXIDES ure 8. T h e s e oxides a r e ds, diameter in microns of particle of average surface (3) S , specifio surface in square meters per gram made by the electrothermic ZnO A ZnO B ZnO C process and are of the same ds 0.42 d3 0.66 d3 0.93 S 2.59 S 1.70 s 1.20 chemical purity. Figures 9, 10,11, and 12 give the usual physical test data on these rubber compounds and show Figure 13 shows the horizontal loads, or deflecting forces, correlation of hardness, tensile, and abrasion with particle on the specimens plotted against time of test in minutes. size. These tests were stopped a t initial failure and not carried to blowout, as shown on Figure 7 . The horizontal load, or TABLEXI. FORMULA FOR HIGH-ZINO STOCKB flexing force, increases a t different rates for the various Rubber 100.0 stocks and indicates a marked stiffening of the compounds. Sulfur 4.0 Di-o-tolylguanidine 1.4 This flexing force could not be measured on any of the previous Zinc oxide 160.0 Gas black 9.0 machines. Figure 14 shows the progressive increase in vertical com-411 apeciinens cured 65 minutes at 286' F. (141.1° C.).
INDUSTRIAL AND ENGINEERING CHEMISTRY
64
,
x
f 0
-
1
OUPONT ABRASIONS I I I
I
I
I
I
I I
I
I I
I
I
I
I
CB I
TEU
ILE
BPE K
I
iL
3
0
30 Cure in Minrtes @
4.
40
286 9. (141.1 T)
FIGURE 9. PHYSICAL TESTDATAFOR ZINC OXIDES A, B, AND c Abrasion index =
cc. loss per hp.-hr. for ZnO A cc. loss per hp.-hr. for comparative ZnO
(
)x
1000
Cure In Minutes 0 141 "C. FIGURE10. PHYSICAL TESTDATA Zinc oxides A, B, and C
Vol. 7, No. 1
were held constant, the horizontal load increased during t h e test. T h e s e d a t a indic a t e t h a t t h e inc r e a s e in horizontal load is not due t o any c h a n g e in shape of the specimen during the test, but to a structural change which takes p l a c e in the rubber. STEPPED INC R E A S E HORIZONT A L L O A DTEST.
F i g u r e 17 a n d T a b l e I11 show d a t a o n the vario u s z i n c oxides when compared by t h e s t e p p e d increase h ori z o n t a1 load test. T h e conditions of horizontal loading are exactly the same for the threestocks, and deflections are dependent on modulus and stiffness of the Cure i n Miwtes 0 141 OC. compounds. The FIGURE 12. PHYS~CAL TESTDATA temperature a t the Zinc oxides A, B, and C Cute in Minutes 0 141 'C, c e n t e r of the test specimen has been FIGURE 11. PHYSICAL TESTDATA plotted against Zinc oxides 9,R , and C time. Zinc stocks B a n d C show a rapid i n c r e a s e in temperature a t the start of the test due to greater deflection produced b y t h e horizontal load on these softer stocks. (Figures 11and 12). In this method of t e s t i n g the stock containing c o a r s e p a r t i c l e size zinc l i m e in Minutes Time in Minutes FIGURE14. CONSTANTHORIZONTAL DEFLEC- oxide C does n o t FIGURE13. CONSTANT HORIZONTAL DEFLECresist breakdown as TION TEST TION TEST well as stocks conZinc oxides A, B, and C Zinc oxides A , B , and C taining zinc oxides A Bnd B. .___.. The effect of cure on breakdown, when EFFECT OF CURE. pression (decrease in height of test specimen) which would normally indicate a softening of the stock. Figure 13, how- specimens are tested by the constant horizontal deflection ever, shows that the compound actually stiffens during test, test method, is shown on Figures 18 and 19. The optimum which indicates that the flattening is due not to a softening cure as regards time required to break down a specimen is of the stock, but probably to a continuous change in the 85 minutes, while the optimum cure, as regards maximum tensile strength, is only 15 minutes. In general, the underpermanent set of the stock as the test progresses. CONSTANT VERTICALCOMPRESSION TEST. Figure 16 shows cures suffer greater initial vertical compression and require a modification of the constant horizontal deflection test. more horizontal load a t the finish of the test than either the I n this case the vertical compression was maintained constant optimum or overcures. EFFECTOF CHANGESI N VOLUMELOADING.Results of and the vertical load was measured on a platform scale similar to the horizontal load scale. It is interesting to note that al- tests on rubber compounds with a variation in the zinc oxide though the vertical compression and horizontal deflection content, when tested under constant horizontal deflection
ANALYTICAL EDITION
January 15, 1935
t e s t conditions, are shown in Figures 20, 21, a n d 22. The zinc oxide in t h e f o r m u l a , T a b l e 11, w a s varied by 5 volumes e i t h e r side of the standard, which is 26.7 volumes on 100 p a r t s ( b y weight) of rubber. To m a i n t a i n the same h o r i z o n t a1 d e f 1e c t io n, t,h e higher loaded stocks require g r e a t e r horizontal load or deflecting force than the lower loaded stocks. In Figure 22 the horizontal l o a d is plotted against t h e increase i n v e r t ic a1 compression with the time intervals noted on the curves. If the area under the curve be considered a s a m e a s u r e of e n e r g y expended, the higher volume loadings r e q u i r e more work to cause failure. EFFECT
65
r
lime i n H i d e s
FIGURE16. CONSTANT VERTICAL COMPRESSION TEST
Time in Minutes
FIGURE15. CONSTANT HORIZONTAL DEFLECTION TEST
Zinc oxides A and B
Zinc oxides A, B, and C
I
I
I
W
32
IO
20
Tme in Pinutes
FIGURE17. STEPPEDINCREASE HORIZONTAL LOAD TEST Zinc oxides A, B, and C
b
I
I
IoTis in Mi&
O'
x
FIGURE 18. EFFECT OF CURE Zinc oxide A
OF
CHANGESIN VERTICAL L O A D . FigC. ure 23 shows t h a t an increase in vert i c a l l o a d on a specimen results in a shortening of the time required to produce failure. With an i n c r e a s e in vertical load on the specimen, less h o r i z o n t a l load is r e q u i r e d a t the start of a test. At FIGURE 19. EFFECTOF CURE FIGURE20. CHANGESIN VOLUMELOADING Zinc oxide A the finish, however, Zinc oxide A a g r e a t e r horizontal load is reauired for the same iorisontal deflection. COMMERCIAL STOCKS EFFECT OF CHANGES IN HORIZONTAL DEFLECTION.Breakdown is produced in a rubber specimen by running under The machine, to be of commercial value, must show good vertical load and horizontal deflection. An increase in hori- correlation between laboratory and service tests. To study zontal deflection subjects the specimen to greater stresses this correlation the authors obtained from several rubber and shortens the time required for a test. Conversely, a de- companies carcass and solid tire stocks with ratings of good crease in the deflection is reflected by a decrease in flexing and poor as regards resistance to blowout in service. The force and increase in running time. Results of tests using dif- laboratory tests show that excellent correlation is obtained. ferent horizontal deflections are shown on Figure 24. Al- Results obtained on some representative commercial stocks though the difference between the low and medium deflec- are shown in Figures 25 to 30. tions is the same as that between the high and medium deCARCASS STOCKS. Two carcass stocks were compared by flections, the variation in the flexing load-time rate is ap- the constant horizontal deflection test method, as it was felt proximately 4 to 1. that this method of testing would most nearly approach
f
I
-
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
66 I
I
I I
I
I
I
\x\
Vol. 7, No. I
I
I\
\ I
\ i
2 d
u
E 8 7 5 22.2 w ~
31.7 Vo umes
26. Vol.
rime in Minutes
>
IN VOLUME LOADING FIGURE21. CHANGES
Time in Minutes
Zinc oxide A
HORIZO~TAL DEFLECTION TEST FIGURE 25. CONSTANT Commercial carcass compound
Tim i n Minutes IN HEIGHT OF TESTSPECIMEN FIGURE26. CHANGE
Commercial carcass compound
Change in Vertical Compression
FIGURE22. CHANGES IN VOLUME LOADING Zino oxide A
0
O0 Time in Mimutes
80
IO0
.-
Time i n Minutes
FIGURE 27. CONSTANT HORIZONTAL DEFLECTION TEST FIGURE 23, EFFECTOF CHANGES IN VERTICAL LOAD Commercial solid tire stocks Zino oxide B
Tis i n Minutes
FIGURE24. VARIATION IN HORIZONTAL DEFLECTION
Zino oxide B
actual service conditions. Under, optimum, and overcures were made on each stock, With essentially the same applied flexing force, compound D (good road test) resists failure for a longer time than compound E (poor road test), which checks the manufacturers' road tests. SOLIDTIRE STOCKS. The results of tests on two solid tire stocks, F (good) and G (poor), when run by the constant horizontal deflection test method are shown on Figures 27 and 28. These two stocks would be rated equal if considered on a time basis alone, but when the horizontal load or deflecting force is a consideration, stock F is decidedly superior, since it runs for the same length of time under a much greater load. On Figure 28 the vertical compression is plotted against time. If the time for a 0.762-cm. (0.30-inch) drop in vertical compression is used as the end point, stock G
January 15, 1935
ANALYTICAL EDITION
reaches this in 35 minutes, and stock F in 23 minutes. It is evident that machines which evaluate on vertical compression and time only give results which may be greatly in error. C
e
400 200 ‘C.
f = Good Road Test G 2 Poor Rod Test I
67
SUMMARY A new machine for evaluating breakdown characteristics of rubber compounds, described above, not only measures the flexing forces a t all times, but also indicates the point of initial failure, accurately, before complete destruction of the test specimen takes place. The theoretical value of the machine has been revealed by the indication of an unexpected structural change which takes place in the rubber during flexing. This change manifests itself in a marked stiffening of the stock which increases until initial failure occurs. The practical value of the machine has been demonstrated by its ability to simulate different types of service conditions, as shown by the excellent correlation of the authors’ tests with the manufacturers’ road tests on commercial compounds.
LITERATURE CITED FIGURE29. STEPPEDINCREASE HORIZONTAL LOAD TEST Commercial solid tire stocks
WTo duplicate service conditions as nearly as possible, it was felt that the stocks should be tested under the same loading conditions. The deflections would then be dependent on the modulus and stiffness of the compounds. The stepped increase horizontal load test was used and temperatures were taken a t the center of the specimen and plotted against time (Figure 29). Both specimens were subjected to the same system of loading, which was 3.2 kg. (7 lb.) at the start increased by 4.1 kg. (9 lb.) a t six 5-minute intervals. Stock G failed in 30 minutes, while stock F did not fail even after 90 minutes of testing. At the end of 90 minutes the temperature was dropping, indicating that failure due to heat was impossible. The stocks were then compared under the matched horizontal load conditions of testing. Both stocks were first run in the regular way, as shown on Figure 27, with a vertical load of 261 kg. (575 lb.) and a horizontal deflection of 0.533 cm. (0.210 inch). Stock G was again tested and the horizontal load adjusted by means of the handwheel to match the greater load of stock F. Stock G failed in considerably less
Tim in Hinubs
FIGURE 30. MATCHED HORIZONTAL LOADTEST Commercial solid tire stocks
time than stock F, which again checks the manufacturers’ road tests. Stock E’ was again tested and the horizontal load adjusted to match the lesser load required by stock G. Stock F withstood the less severe conditions and the specimen started to decrease in temperature after 60 minutes, indicating that no failure due to heat would occur. This test is recorded on Figure 30.
(1) Abbott, IND. E m . CHEM.,20, 853-7 (1928). (2) Cooper, Ibid., Anal. Ed., 5,350-1 (1933).
(3) Perrott, G. St. J., and Kinney, S. P., J. Am. Ceramic Soc., 6.
417-25 (1923). (4) Schopper, Louis, Catalog 415, p. 25, Leipzig, Germany; American
agent, Testing Machines, Ino., New York, N. Y . RECEIVED September 15, 1934. Presented before the Division of Rubber Chemistry a t the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14, 1934.
Wash Bottle for Quantitative Work EDWINJ. DEBEER 1254 North 28th St., Philadelphia, Pa.
I
T FREQUENTLY happens in analytical work that a precipitate must be washed or transferred from one container to another with a limited quantity of reagent. By means of the device illustrated, a measured amount of liquid. may be directed in such a way as to aid in stirring up and dislodging the precipitate. The tube A is sealed into the bottom of the inner reservoir and the end cut off a t r i g h t angles. A small rounded section of glass rod is dro ped into the inverted tube anzthe end carefully and evenly heated with a small hot flame until the contracting glass has almost sealed the opening. This simple valve will permit pressure to be built up within the inner reservoir, so that its contents may be blown out. It will also prevent the flow of liquid from the outer t o the inner reservoir following sudden changes in pressure. A small vent, indicated at E, may be cut into the stopper in case too much air escapes through the valve. The d i a m e t e r of the inner reservoir and the dedh t o which the delivery t u b e ; B, extends, govern the volume of liquid expelled a t a n y one time. The inner reservoir is filled by pinching the rubber connection, C, thus shutting off the delivery tube, and applying suction at the mouthpiece. Excess liquid will drain back into the inner reservoir. It is emptied in the usual manner, care being taken not t o incline the wash bottle too much. R ~ C ~ I VOctober ED 31, 1934.
